/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.harmony.jndi.internal;

/**
 * Identifies the simplest URL syntax:
 * <code>{scheme}:{scheme specific part}</code>.
 */
public class UrlParser {

	/**
	 * Returns an URL's scheme part, in lower case. If the url is not a valid
	 * URL, null is returned.
	 * 
	 * @param url
	 *            a url string
	 * @return the URL's scheme part, in lower case. If the url is not a valid
	 *         URL, null is returned.
	 */
	public static String getScheme(String url) {
		if (null == url) {
			return null;
		}
		final int colPos = url.indexOf(':');
		if (colPos < 0) {
			return null;
		}
		final String scheme = url.substring(0, colPos);
		char c;
		boolean inCharSet;
		for (int i = 0; i < scheme.length(); i++) {
			c = scheme.charAt(i);
			inCharSet = (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z')
					|| (c >= '0' && c <= '9') || c == '+' || c == '.'
					|| c == '-' || c == '_';
			if (!inCharSet) {
				return null;
			}
		}
		return scheme;
	}

	/*
	 * Prevent instantiate.
	 */
	private UrlParser() {
		super();
	}

}
